A randomized controlled single-blind trial was performed to compare lumbo-sacral selective posterior rhizotomy (SPR) followed by intensive physiotherapy, with intensive physiotherapy alone in improving motor function in children with spastic diplegic cerebral palsy. Fifteen patients were randomly assigned to each treatment modality. Patients in the SPR group had rhizotomy within 1 month, followed by intensive outpatient physiotherapy for 9 months. Patients assigned to physiotherapy alone had identical intensive physiotherapy. There was a statistically significant and clinically important difference in improvement in motor function in favor of the SPR group, with a mean increase in total Gross Motor Function Measure (GMFM) score of 11.3% at 9 months for the SPR group compared with 5.2% for the physiotherapy-only group (P = 0.007). Significant improvements in spasticity (P < 0.001) and range of movement (P < 0.001) were noted in the SPR group compared to the physiotherapy-only group. The results indicate that the improvement in motor function after SPR is more than can be explained by the associated intensive physiotherapy.